Pirates used Eye-Patches so that They get their Eyes accustomed to the Dark, They would adjust more quickly,
For example, They would cover one Eye & once it's Night or They are going to a Dark Place (Including inside the Ship), They would switch Eyes,
Zoro being One-Eyed was said by Oda to have been Planned since before OP even started, meaning it's very crucial for Story,
And based on what i explained above, this means that his Closed Eye is meant for another Place
This is further foreshadowed by Zoro's Weakness with Directions, do you know what else is Bad with Directions in One Piece? Compass or Log Pose that aren't where they belong,
A Normal Compass doesn't work in Grand Line, you need a Log Pose, and even that doesn't work in New World as you needed an Upgraded One (with Three Needles instead of One),
So Zoro's Eye & Gag is actually revealing to us that Zoro doesn't belong in this World, his Vision & Sense of Direction belongs in another place, and i don't really need to prove any of this, the guy is Asura (Three Heads using Nine Swords, which makes him like Upgraded Form of NW Log Pose) & everything about him is related to Afterlife (Even Shinigami paid him a visit), and He even said that i'm gonna become King of Hell
OP World is much more than it seems, there are countless Hints that there is an Underworld Version of it & also a Heaven Version of it, for example i won't be surprised if Holy Knights & Gorosei can Teleport using this Underworld which was also shown when Giant Straw Hat was revealed, while Heaven World is Ancient Kingdom
Elbaph is just a Mini-Version of The World, that's why Oda re-created that Scene of Shanks in a Bar with a Kid asking to join his Crew.